Radon

Radon (Rn) is a noble gas with atomic number 86. It has no stable isotope and no characteristic isotopic composition on Earth, so it has no standard atomic weight; its longest-lived isotope has mass number 222. Its electron configuration is [Xe] 4f14 5d10 6s2 6p6, which gives it 8 valence electrons.

Radon key data

Symbol	Rn
Atomic number	86
Mass number (longest-lived isotope)	222
Protons	86
Neutrons (longest-lived isotope, radon-222)	136
Electrons (neutral atom)	86
Valence electrons	8
Category	Noble gas
Period	6
Group	18
Block	p-block
Noble gas notation	[Xe] 4f14 5d10 6s2 6p6
Full electron configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6
Electrons per shell	2, 8, 18, 32, 18, 8

Mass number: IUPAC CIAAW radioactive elements, from NUBASE2020.

Measured properties of radon

From PubChem, the US National Institutes of Health. Public domain. PubChem’s periodic table gives no value for the rows not shown. The first ionisation energy is the value for radon from the NIST Atomic Spectra Database, in place of PubChem’s 10.745 eV.

Melting point	202 K (−71.15 °C), 93rd of 103 by melting point
Boiling point	211.45 K (−61.7 °C), 84th of 93 by boiling point
Density	0.00973 g/cm³, 86th of 96 by density
State at room temperature	Gas
Van der Waals radius	220 pm, 35th of 99 by atomic radius
First ionisation energy	10.7485 eV (1037.07 kJ/mol), 13th of 102 by first ionisation energy
Common oxidation states	0
Discovered	1900

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Radon electron configuration

The full electron configuration of radon is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6. With the noble-gas core collapsed it is [Xe] 4f14 5d10 6s2 6p6, and the outermost subshell is 6p6.

Bohr model of radon (Rn): a nucleus and six shells holding 2, 8, 18, 32, 18 and 8 electrons from the inside out. — Bohr model of radon (Rn). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Orbital box diagram of radon (Rn), [Xe] 4f14 5d10 6s2 6p6, with the xenon core drawn as one bar: one box per orbital, filled by Hund’s rule, showing every orbital drawn holds a pair of electrons. — Orbital diagram of radon (Rn). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one radon atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

one atom = 222 / (6.02214076 × 10²³)
= 3.6864 × 10⁻²² g

Atoms in one gram

atoms per gram = 6.02214076 × 10²³ / 222
= 2.7127 × 10²¹ atoms

Radon has no standard atomic weight, because it has neither a stable isotope nor a characteristic isotopic composition on Earth. The figure used above is the mass number of radon-222, so treat these as nominal.

Radon on the periodic table

Radon is in period 6, group 18, in the p-block.

The other elements of group 18 are helium, neon, argon, krypton, xenon and oganesson.